1. Field
One embodiment of the invention relates to a 2-2 pulldown signal detection device which detects a pulldown signal generated by a 2-2 pulldown mode from cinema films, etc. and an improved 2-2 pulldown signal detection method.
2. Description of the Related Art
As is generally known, in the PAL (phase alternation by line color television) image signal mode, which is generally known as television broadcast waves, screen flicker is mitigated by interlacing images with an interlaced scan and increasing the equivalent number of images per second.
Meanwhile, recently, television monitors with slim and large screens have been spreading widely, using liquid crystal display devices and plasma display devices, etc. However, when using such display devices and displaying image signals of an interlaced scan for each scan line just as they are, screen luminance decreases and the image becomes not too worthy of admiration.
Consequently, in such display devices, noninterlaced mode is used to display images. That is, if displaying an image signal of an interlaced scan on a display device such as a liquid crystal display device, a conversion circuit is required so as to convert the image signal of the interlaced scan into an image signal of noninterlaced mode.
Herein, in image signals of standard television modes such as PAL mode, etc., image signals generated based on images of cinema film may be included. In other words, cinema film has 24 segments per second, on the other hand, image signals of standard television mode have image signals of interlaced scans at 25 frames per second (50 fields per second).
Consequently, images of cinema film are converted by a 2-2 pulldown method into image signals of standard television mode with interlaced scans. The image signals of interlaced scans generated from cinema films using such a method is referred to as pulldown signal.
For example, in the 2-2 pulldown method, image signal of noninterlaced mode with 24 Hz frame frequency is generated by interlacing cinema films, and one frame of this generated image signal is converted to support two fields. And, this converted field signal repeats odd fields and even fields alternately.
Incidentally, in a conversion circuit which converts pulldown signals into image signals of noninterlaced mode, it is important to detect whether the input image signal is a pulldown signal, and if it is a pulldown signal, conduct a conversion process into noninterlaced mode so as to reproduce the original. In unexamined patent publication bulletin 2002-290927, a structure to detect whether an input image signal is a pulldown method is disclosed.
However, in the pulldown signal detection measures described in unexamined patent publication bulletin 2002-290927, when it comes to a momentarily stationary scene with a 2-2 pulldown signal (several fields), it is decided that it is not a 2-2 pulldown signal, and cannot stably detect a 2-2 pulldown signal.
Also, even when it comes to a scene which is momentarily stationary, if it is made possible to continue the results of detecting that is 2-2 pulldown signal, conversely, it may sometimes miss a small motion and falsely detect that is a 2-2 pulldown signal, even after the input image signal is no longer a 2-2 pulldown signal.